1. Field of the Invention
The present invention relates to a packet transfer device and a packet transfer method, and particularly to a packet transfer device and a packet transfer method that transmit input packets by using a redundancy configuration of plural systems, and select and output packets for one transmission path at a reception side in a packet transfer network such as an IP network, or Ethernet (registered trademark).
2. Description of the Related Art
A network construction based on a redundancy configuration using an uninterruptible switching technique is known in a packet transfer network, particularly in a network demanding communications in which data are not missing. The following packet transfer method and device using Ethernet (registered trademark) are known in the above type of technique.
A packet transmitting function part of a packet transfer device at a transmission side creates two copies from each of received packets, adds each of these copied packets with a sequence number for identifying the same transmission order, further adds each of the copied packets with an identifier for identifying a transmission path, and then transmits these copied packets to different transfer paths, respectively. A packet receiving function part of a packet transfer device at a reception side receives the packets (the packets transferred from the transmission side) by two receiving units, and identifies packets having the same information and the transmission order thereof on the basis of the sequence numbers and the identifiers of the received packets. Furthermore, the packet receiving function part selects one of the packets having the same transmission order, transmits the selected packet to the downstream side and discards the other packet (non-selected packet). Or, when only one of the packets arrives at the reception side, the packet receiving function part transfers the arrival packet to the downstream side, thereby implementing an uninterruptible switching function (see JP-A-2005-102157 (hereinafter referred to as “patent document 1”), for example).
Furthermore, according to another uninterruptible switching technique, a packet transmitting function part of a packet transfer device at a transmission side creates two copies from each of received packets, adds each of the copied packets with a predetermined identification signal and then transmits the copied packets to different transmission paths. Furthermore, a packet receiving function part of a packet transfer device at a reception side receives the packets by two receiving units, and detects the difference in arrival time between the packets received by both the two receiving units on the basis of the identifiers of the packets. On the basis of the arrival time difference, the packet receiving function part applies a delay to each packet of an earlier arrival packet group (i.e., each of packets which are transmitted through one of the transmission paths and arrive at the reception side earlier than the corresponding packets transmitted through the other transmission path) to eliminate the time difference, whereby the uninterruptible switching function is implemented (see JP-A-4-243335 (hereinafter referred to as “patent document 2”), for example).